Prolonged single seizures (status epilepticus) and repeated seizures over time can be damaging to the brain and trigger or exacerbate epileptogenesis, the process culminating in spontaneous seizures/epilepsy. Endogenous, non-pharmacologic neuroprotective mechanisms can prevent cell death during acute stress including that of seizures. In a mouse model of epileptic tolerance, developed by the applicants, we show that brief, generalized seizures activate an endogenous protective programme in brain which strongly reduces neuronal death after a later episode of status epilepticus. The molecular mechanisms induced by such seizure preconditioning hold the key to novel routes for neuroprotection and, possibly, antiepileptogenesis. Our data show that preconditioning seizures alter expression of a selection of microRNAs (miRNAs), small non-coding RNAs which are post-transcriptional regulators of protein translation, and their biogenesis machinery. We have preliminary data showing interference with miRNA 184 and 204 prevents preconditioning-mediated neuroprotection against status epilepticus, indicating they are functionally required for epileptic tolerance to manifest. Our CENTRAL HYPOTHESIS is that the neuroprotection of epileptic tolerance is mediated by seizure-preconditioning via induction of select miRNAs. We propose the following Specific Aims: Aim 1. Characterize the hippocampal miRNA transcriptome after seizure-preconditioning and characterize the effects of seizure-preconditioning on miRNA biogenesis components;Aim 2. Characterize the preconditioning-induced miRNA uptake to Argonaute/RISC and identify their in situ mRNA targets;Aim 3. Demonstrate the functional requirement of miRNAs 184 and 204 in mediating tolerance;Aim 4. Characterise the long-term effects of modulating preconditioninginduced miRNAs on epilepsy